Hybrid composite structures for ballistic protection

ABSTRACT

The present invention relates to hybrid composite structures with improved ballistic protection properties. More specifically, the present invention relates to hybrid composite structures with improved ballistic protection properties that comprise at least three sub-layers.

FIELD OF THE INVENTION

The present invention relates to hybrid composite structures with improved ballistic protection properties. More specifically, the present invention relates to hybrid composite structures with improved ballistic protection properties that comprise at least three sub-layers.

BACKGROUND OF THE INVENTION

The recent anti-terrorism war in Iraq and other US military missions have demonstrated the advantages of well-prepared, small, mobile and lethal combat forces that can rapidly respond to a broad range of tasks in limited regional conflicts. The new strategy of US military forces presents an urgent need for “leap frogging” technologies. Weight reduction for present and future army combat systems is critical to the rapid deployment of military contingencies under the requirement of this new strategy. Traditional armor vehicle is protected by heavy metal armor which not only produces fuel energy and transportation problems, but also reduces the mobility and speed of the vehicle significantly. Therefore, there is a need to develop lighter structural components with better blast resistance, so that the safety of soldiers and operational efficiency can be both improved.

To reduce the weight of armor, research is being conducted in the area of lightweight composite armor, from which heavy metal components are replaced by lighter ceramic and fiber-reinforced composites. In these types of proposed armor structures, a ceramic out-layer blunts a projectile and dissipates the load over a wide area; while a composite backing plate slows and catches the projectile, or pieces of projectile and the ceramic layer until the final layers exceed their tensile strength to fail. The major portion of the impact energy is absorbed by the composite backing plate which is controlled largely by the energy absorption capacity of fibers (see Hogg, P. J., Composites for Ballistic Application, Composites Processing 2003, CPA, Bromsgrove, U.K., 21 Mar. 2003). Due to intensive fracture and delamination in composite backing plate after impact, the existing type of two-layer (i.e., ceramic tile-composite plate) composite armor has poor structure integrity and less multi-hit resistance. To improve the multi-hit capacity of the armor, a layer of rubber is often used between ceramic tile and composites plates (see Gama, B. A., Bogetti, T. A., Fink, B. K., Yu, C., Claar, T. D., Eifert, H. H., and Gillespie, J. W. Jr., Aluminum foam integral armor: a new dimension in armor design, Composite Structures, Vol. 52, 381-395 (2001)). However, since rubber is compliant, the inclusion thereof reduces the stiffness of the resulting structure dramatically. Accordingly, a need exists to develop a feasible multi-layer hybrid armor composite solution with better impact resistance and high energy absorption that will lead to a safer and lighter armor system.

Light weight composite structures, as well as hybrid composite structures that withstand high energy absorption, are required for ballistic protection (armor) of military vehicles. Also of concern is the need for mobility and transportability of such composite structures (or even the vehicles and/or persons who might use such composite structures).

SUMMARY OF THE INVENTION

The present invention relates to hybrid composite structures with improved ballistic protection properties. More specifically, the present invention relates to hybrid composite structures with improved ballistic protection properties that comprise at least three sub-layers.

In one embodiment, the present invention relates to designs for ballistic protection based on various materials and fiber architectures, that are achieved using preliminary design analysis and selection of armor composite structure. These armor composite structures achieve performance under ballistic impact as shown using numerical finite element simulation. The result is a hybrid composite structure or structures with improved ballistic protection properties.

In another embodiment, the present invention relates to hybrid composite armor structures comprising at least three layers. In one embodiment, the three layer hybrid composite armor of the present invention includes at least one ceramic and/or ceramic tile layer, at least one backing layer, and at least one intermediate layer positioned between the at least one ceramic layer and the at least one backing layer. In one embodiment, the at least one backing layer is a composite layer.

In still another embodiment, the hybrid composite armor of the present invention comprises at least one hard ceramic face/layer to blunt a projectile, at least one backing layer, and at least one intermediate layer positioned between the one or more face layers and the one or more backing layers. Either the one or more intermediate layers or the one or more backing layers is/are designed to primarily provide structure integrity and to impart multi-hit capacity to the armor of the present invention. The other layer or layers is/are designed to primarily absorb high impact energy. Such a design has numerous benefits over current composite armor including, but not limited to, the utilization of materials more efficiently, an increase in both structural integrity and the ability to withstand multiple impacts/hits. Accordingly, the hybrid composite armors of the present invention contain armor structures with excellent impact resistance, high energy absorption, and adequate thermal properties.

In still another embodiment, the present invention relates to a hybrid composite armor structure comprising: at least one face layer, the face layer being formed from a ceramic layer; at least one backing layer, the backing layer being formed from at least one composite; and at least intermediate layer, the intermediate layer being positioned between the at least one face layer and the at least one backing layer.

In still another embodiment, the present invention relates to a hybrid composite armor structure comprising: at least one face layer, the face layer being formed from a ceramic tile layer; at least one backing layer, the backing layer being formed from at least one laminated composite or chain composite; and at least intermediate layer, the intermediate layer being positioned between the at least one face layer and the at least one backing layer, where the one or more intermediate layers are formed from a braided composite, stitched composite, or a foam layer.

In still another embodiment, the present invention relates to a hybrid composite armor structure comprising: at least one face layer, the face layer being formed from an aluminum ceramic tile layer; at least one backing layer, the backing layer being formed from at least one laminated composite or chain composite; and at least intermediate layer, the intermediate layer being positioned between the at least one face layer and the at least one backing layer, where the one or more intermediate layers are formed from a braided composite, stitched composite, or a aluminum foam layer wherein the composite used in any one or more of the composite layers is at least one fiber-reinforced composite.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a hybrid composite armor system for ballistic protection;

FIGS. 2 a and 2 b are illustrations of novel composites that can be used as backing materials in the composite armors of the present invention;

FIGS. 3 a and 3 b are illustrations of existing armor composite structures;

FIGS. 4 a to 4 f are cross-sectional drawings of hybrid composite armor structures in accordance with the present invention;

FIG. 5 is an analytical model of a multilayered composite armor system in accordance with the present invention;

FIG. 6 is an illustration of the peanut-shape damage area of the laminate;

FIGS. 7 a to 7 c are illustrations of a braided composite panel after impact;

FIGS. 8 a and 8 b are illustrations of a braided composite panel after impact; and

FIG. 9 is a finite element modeling of a ballistic impact of braided composite panel.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to hybrid composite structures with improved ballistic protection properties. More specifically, the present invention relates to hybrid composite structures with improved ballistic protection properties that comprise at least three sub-layers.

In one embodiment, the present invention relates to designs for ballistic protection based on various materials arid fiber architectures, that are achieved using preliminary design analysis and selection of armor composite structure. These armor composite structures achieve performance under ballistic impact as shown using numerical finite element simulation. The result is a hybrid composite structure or structures with improved ballistic protection properties.

In another embodiment, the present invention relates to hybrid composite armor structures comprising at least three layers. In one embodiment, the three layer hybrid composite armor of the present invention includes at least one ceramic and/or ceramic tile layer, at least one backing layer, and at least one intermediate layer positioned between the at least one ceramic layer and the at least one backing layer. In one embodiment, the at least one backing layer is a composite layer.

In still another embodiment, the hybrid composite armor of the present invention comprises at least one hard ceramic face/layer to blunt a projectile, at least one backing layer, and at least one intermediate layer positioned between the one or more face layers and the one or more backing layers. Either the one or more intermediate layers or the one or more backing layers is/are designed to primarily provide structure integrity and to impart multi-hit capacity to the armor of the present invention. The other layer or layers is/are designed to primarily absorb high impact energy. Such a design has numerous benefits over current composite armor including, but not limited to, the utilization of materials more efficiently, an increase in both structural integrity and the ability to withstand multiple impacts/hits. Accordingly, the hybrid composite armors of the present invention contain armor structures with excellent impact resistance, high energy absorption, and adequate thermal properties.

The ballistic protection capability of a composite structure is commonly achieved by absorbing the kinetic energy of a projectile through a plastic deformation or a fracture process. It requires that the components of the structure have excellent impact resistance and high energy absorption, as well as lighter weight for the efficient transportation and deployment.

As is noted above, the present invention is directed to new hybrid composite armor structures that comprise at least three layers (e.g., one or more ceramic and/or ceramic tile layers, one or more backing layers, and one or more intermediate layers positioned between the one or more facing layers and the one or more backing layers, see FIG. 1). In one embodiment, the new hybrid materials consists of a hard ceramic face layer to blunt the projectile and a combination of a backing layer and an intermediate layer, the intermediate layer being positioned between the hard ceramic face layer and the backing layer. In this embodiment, one layer in the intermediate layer/backing layer combination is designed to primarily provide structural integrity and multi-hit capacity of the armor; and the other layer is designed to absorb high impact energy. Either layer can provide either function in the intermediate layer/backing layer combination, thus the present invention is not limited to just one design.

As is also noted above, such a design has numerous benefits over current composite armor including, but not limited to, the utilization of materials more efficiently, an increase in both structural integrity and the ability to withstand multiple impacts/hits. Accordingly, the hybrid composite armors of the present invention contain armor structures with excellent impact resistance, high energy absorption, and adequate thermal properties. In addition, materials such as braided and chain composites can be employed as the one or more backing layers and as the one or more intermediate layers. Such composites can be selected independently of one another. Thus, the present invention is not limited to designs that only use one type of composite. Rather, any combination of different composites can be utilized. Therefore, the present invention makes possible novel combinations of material systems that permit the construction of numerous hybrid composite structures with excellent ballistic resistance.

Different types of ceramic tile can be used interchangeably in the present invention. Even though the examples use aluminum ceramic tile as the ceramic face layer, the present invention is not limited thereto.

The materials used for the one or more intermediate layers and the one or more backing layers in the present invention are, in one embodiment, located underneath the ceramic face layer. In one embodiment, the one or more intermediate layers and the one or more backing layers of the present invention are independently formed from fiber-reinforced composites. Fiber-reinforced composites are advantageous in that they are light weight, high in strength, have high stiffness to weight ratios, and possess the ability to absorb a high amount of energy (i.e., high energy absorption). The ability of a composite to absorb a large amount of energy (e.g., impact energy) is primarily determined by the nature of the reinforcing fibers. In one embodiment, the present invention utilizes fiber systems with good ballistic performance. These include glass (S- and R-glass), aramid (commercial name KEVLAR® or TWARON®), high performance polyethylene (HPPE) (commercial name SPECTRA® or DYNEEMA®), polybenzoxazole (PBO), M5 fibers formed from polypyridobisimidazole, or combinations of two or more thereof.

Besides the type of fibers used to form the fiber-reinforced backing layers, the fiber architecture also plays a role in energy absorption and ballistic protection. Braided composites showed excellent damage tolerance (see Roberts, G. D., Pereira, J. M., Revilock, D. M., Binienda, W. K., Xie, M., and Braley, M., Ballistic impact of braided composites with a soft projectile, NASA/TM-2004-212973 (2004)); whereas chain composites could undergo large deformation thus leading to high impact energy absorption (see Cox, B. N., Sridhar, N., Davis, J. B., Mayer, A., McGregor, T. J., and Kurtz, A. G., Chain composites under ballistic impact conditions, International Journal of Impact Engineering, Vol. 24, 809-820 (2000)). Accordingly, in one embodiment of the present invention a hybrid composite armor utilizes one or more intermediate layers and one or more backing layers selected independently from chain composites, braided composites, or a combination of chain and braided composites. The use of such composites in combination with the other layers of the hybrid composite armor made in accordance with the present invention permits the manufacture of armor with improved ballistic protection properties.

Although a matrix plays a somewhat lesser role in energy absorption of composite materials under ballistic impact, studies have indicated that there are some differences in the capacity/capability to absorb energy among various matrices. It is known that a polyurethane matrix provides better impact response and crashworthiness (see, e.g., Qiao, P. Z. and Yang, M. J., Fatigue Life Prediction of Pultruded E-glass/Polyurethane Composites, Journal of Composite Materials, Vol. 40(9), 815-837 (2006)) when compared to a conventional polymer matrix (e.g., epoxy, phenolic, polyester, or vinyl ester matrices). Besides polyurethane, a matrix formed from a polycarbonate can also be used in a hybrid armor formed in accordance with the present invention. This is because polycarbonates have the highest impact resistance among thermoplastic polymers.

Based on the above backing materials plus the fiber and matrix systems, the following five types of composites are within the scope of the present invention and are used to form/manufacture hybrid composite armor in accordance with the present invention.

-   -   (1) Conventional laminates: these types of composite materials         are known to those of skill in the art and are generally used as         the backing plate layer in the composite armors of the present         invention.     -   (2) Hybrid composite materials: glass fibers in combination with         other high performance fibers such as PBO and M5 fibers, yield         composite materials having excellent performance both in         structural efficiency and energy absorption.     -   (3) Stitched composites: stitched composites can be used to         contain the damage induced by ballistic impact loading.     -   (4) Braided composites: braided composites (see, e.g., FIG. 2 a)         can tolerate a significant amount of damage caused by a         ballistic impact (see Roberts, G. D., Pereira, J. M.,         Revilock, D. M., Binienda, W. K., Xie, M., and Braley, M.,         Ballistic impact of braided composites with a soft proiectile,         NASA/TM-2004-212973 (2004)). The present invention utilizes         braided composites such as, but not limited to, quasi-isotropic         tri-axial braided composites (e.g., 0°/±60°) (see Binienda, W.         K., High energy impact of composite structures—Ballistic         experiments and explicit finite element analysis, Report,         submitted to NASA Glenn Research Center, The University of         Akron, Akron, Ohio (2004)) to, among other things, improve the         multi-hit capability of an armor designed in accordance with the         present invention.     -   (5) Chain composites: chain composites (see FIG. 2 b) are a new         class of composites with exceptionally high specific energy         absorption capacity under tensile loading (much higher than         conventional composites). Accordingly, the present invention         utilizes these composites to increase the energy absorption         ability of armor designed in accordance with the present         invention.

Besides the above viable composites, aluminum foam can also be used as an intermediate layer in a hybrid composite armor in accordance with the present invention.

Conventional modern light-weight composite armor consists of a ceramic facing plate and a more flexible backing layer (see FIG. 3 a). The ceramic facing layer blunts the projectile and dissipates the load over a wide area; while the flexible backing plate slows and catches the projectile, or pieces of the projectile, and the ceramic until the outermost layers break. During this process, the impact energy is absorbed through the matrix fracture, the fiber shear and compression, tensile elongation and pull-out, and the delamination of the composite backing laminated plate. Intensive fracture and delamination are desirable in armor in order to absorb energy, but undesirable for a structural integrity aspect and multi-hit resistance aspect. To improve the multi-hit capacity of an armor, a layer of rubber is often used between ceramic and composites plates (see FIG. 3 b). However, since rubber is compliant, the inclusion thereof reduces the stiffness of the resulting structure dramatically.

In order to overcome the shortcomings of rubber, the present invention, in one embodiment, utilizes at least one composite layer as one of either the one or more intermediate layers and/or one of the one or more backing layers in a hybrid armor. In one embodiment, the at least one composite layer is a braided or stitched composite layer. These two types of composites effectively reduce the delamination under ballistic impact, and therefore, have excellent impact damage tolerance capacity as shown in ballistic tests. By utilizing this type of composites in hybrid composite structures, the armor will have improved multi-hit resistance. However, prohibiting delamination reduces the energy absorption of the backing plate since delamination plays an important role in energy absorption and reducing the motion of the projectile. Chain composites exhibit large deformation under impact (e.g., up to 60% elongation) which provides superior energy absorption; but they are vulnerable to delamination and have poor damage tolerance. Thus, to overcome the shortcoming of single composites and take advantage of promising aspects of respective materials, a hybrid composite armor is formed in accordance with the embodiments illustrated in FIGS. 4 a to 4 f. In these embodiments, h_(c) is utilized to represent the at least one ceramic face layer, h₁ to represent the at least one intermediate layer, and h₂ to represent the at least one backing layer. For the designs in FIGS. 4 a to 4 f, the backing plate assembly comprises two layers, one intermediate layer (h₁) and one backing layer (h₂). It should be noted that the present invention is not limited to only this structural design. Rather, the present invention can include any combination of intermediate layers with any combination of backing layer.

For the embodiments illustrated in FIGS. 4 a to 4 d, the backing plate assembly comprises one intermediate layer and one backing layer, where the intermediate layer (h₁) is a braided or stitched composite layer that adds to the multi-hit resistance of the armor, and where the one backing layer (h₂) is made of a laminated composite or chain composite layer that is designed to absorb the impact energy. The embodiments of FIGS. 4 e and 4 f substitute the intermediate layer with a layer of aluminum foam. Alternatively, in still another embodiment the present invention could include two intermediate layers (an aluminum foam layer and a braided or stitched composite layer) in combination with one backing layer, a laminated or chain composite layer.

In one embodiment, the present invention contemplates a total of six different novel hybrid composite structures. In these embodiments the present invention comprises at least one layer of aluminum ceramic facing tile, at least one intermediate layer, and at least one backing layer, where the intermediate layer(s) and the backing layer(s) are underneath the at least one layer of aluminum ceramic facing tile. With reference to FIGS. 4 a to 4 f, the following structures are specific embodiments of the present invention. Although it should be noted that the present invention is not limited to solely the embodiments listed below.

-   -   (1) Ceramic/braided/laminate composites (FIG. 4 a);     -   (2) Ceramic/stitched/laminate composites (FIG. 4 b);     -   (3) Ceramic/braided/chain composites (FIG. 4 c);     -   (4) Ceramic/stitched/chain composites (FIG. 4 d);     -   (5) Ceramic/aluminum foam/laminate composites (FIG. 4 e); and     -   (6) Ceramic/aluminum foam/chain composites (FIG. 4 f).

The ballistic impact of a projectile on the multi-layered composite structures of the present invention is a very complex process. Accurate analysis can only be obtained by numerical simulation, such as finite element analysis which is often cumbersome, extremely time-consuming and computationally expensive. Therefore, a simple and efficient analytical model for ballistic impact of multi-layer composite armor will be employed. Some analytical solutions are available in the literature in which two types of composite armors are studied, namely, ceramic/metal plate armor (see Woodward, R. L., A simple one-dimensional approach to modeling ceramic composite armor defeat, Int. J. Impact Engng, Vol. 9, 455-474 (1990)) and ceramic/composites plate (see Navarro, C., Martinez, M. A., Cortes, R., and Sanchez-Galvez, V., Some observations on the normal impact on ceramic faced armors backed by composite plates, International J. Impact Engng., Vol. 13, 145-156 (1991); Chocron-Benloulo, I. S., Sanchez-Galvez, V., A new analytical model to simulate impact onto ceramic/composite armors, Int. J. Impact Engng, vol. 21, 461-471 (1998); and Sanchez-Galvez, V., and Galvez, D. F., Ballistic impact on ceramic/composite armors, In: Jounes N. et al. eds, Structures under shock and impact V. Computational Mechanics Publication; 673-681 (1998)).

The new analytical theory based on the ceramic layer model of Woodward (1990) and composites layer model of Chocron-Benloulo et al. (1998) can be used to analyze the stages I and II of ballistic impact process of a projectile on the proposed hybrid composite armor systems (see FIG. 5). To this end, besides the major assumptions used in Woodward (1990) and Chocron-Benloulo et al. (1998) models, a new simplified assumption can be used where the one of the backing layers is modeled as an elastic-perfect plastic material with the hinge located at the cone base (see FIG. 5). In this way, stage I of the ballistic impact problem described in FIG. 5(a) can be directly solved by using Woodward (1990) model; while stage II can be viewed as a laminate composite subjected to the impact of ceramic cone and the shear-off of a backing layer which can be solved by the Chocron-Benloulo et al. (1998) model. This simplified theoretical model, allows the governing equations to be obtained through conservation of momentum and energy, and the failure is deemed to occur when the fibers or chains in one or more of the backing layers reach their ultimate tensile strain.

The present analytical model allows one to approximately predict the penetration and perforation of the proposed composite structures under ballistic impact and be efficiently used in the parametric study and preliminary analysis.

In order to check the ballistic protection capability of the different hybrid composite structures (see FIG. 4), numerical finite element simulation with LS-DYNA will be carried out for all the design embodiments.

Ceramics and projectiles will be modeled as bi-linear elastic-plastic materials by using material type 3 (MAT_PLASTIC_KINEMATIC), which contains isotropic and kinematic hardening. Strain rate effect is accounted for by using a strain rate dependent factor, and some non-linear rate-dependent material data for polymer composites obtained from the analytical and experimental studies. Composites are modeled by Material type 22 (MAT_COMPOSITE_DAMAGE) based on Chang-Chang failure criterion. Chang-Chang failure criterion combines three failure criteria, namely, fiber fracture, matrix cracking, and compressive failure. When the combined stresses reach a critical value, the composite is deemed to be failed. Aluminum foam is modeled by Material type 26 (MAT_HONEYCOMB) as isotropic or orthotropic material before compaction, of which the stress tensors are uncoupled with zero Poisson's ratio. After full compaction to final volume, the material is treated as perfectly-elastic plastic. The material constants of ceramic, rubber and aluminum foam that define the material model in LS-DYNA can be obtained from the existing experimental data (see Mayseless, M., Goldsmith, W., Virostek, S. P., and Finnegan, S. A., Impact on ceramic targets, J. of Appl. Mech., Vol. 54, 373-378, (1987); Chocron-Benloulo, I. S., Sanchez-Galvez, V., A new analytical model to simulate impact onto ceramic/composite armors, Int. J. Impact Engng, vol. 21, 461-471 (1998); and/or Sanchez-Galvez, V., and Galvez, D. F., Ballistic impact on ceramic/composite armors, In: Jounes N. et al. eds, Structures under shock and impact V. Computational Mechanics Publication; 673-681 (1998)); while the material properties of composites can be obtained through micromechanics data.

In one instance, an inclined lamina approach (see Gu, B. and Xu, J., Finite element calculation of 4-step 3-dimensional braided composite under ballistic perforation, Composites Part B 35, 291-297(2004)) is used to calculate material properties of braided composite materials used.

An eight-node uniform hexahedron solid element is used to model all the proposed plates of the composite armor systems; while the projectile is modeled by six-node tetrahedron solid elements. The ceramic layer (or layers), and the two or more composite backing layers (or plates) are connected by the CONTACT_TIED_SURFACE₁₃ TO_SURFACE element. This element allows the application of two failure criteria, namely, a maximum tensile stress and a maximum shear stress criterion. The CONTACT_ERODING_SURFACE_TO_SURFACE element is used to describe the interaction between the projectile and the ballistic protection composite structure. This element simulates the projectile erosion which is one of the major features of projectile penetration process. Thus, the penetration and perforation of the ballistic impact can be modeled by eroding elements from the projectile surface as well as target structure. LS-DYNA code provides an erosion algorithm through which the erosion process mentioned above can be easily implemented.

The numerical model will be first calibrated with the existing experimental data in literature (see Mayseless, M., Goldsmith, W., Virostek, S. P., and Finnegan, S. A., Impact on ceramic targets, J. of Appl. Mech., Vol. 54, 373-378, (1987); Chocron-Benloulo, I. S., Sanchez-Galvez, V., A new analytical model to simulate impact onto ceramic/composite armors, Int. J. Impact Engng, vol. 21, 461-471 (1998); and/or Sanchez-Galvez, V., and Galvez, D. F., Ballistic impact on ceramic/composite armors, In: Jounes N. et al. eds, Structures under shock and impact V. Computational Mechanics Publication; 673-681 (1998)). Both NATO AP 7.62 mm round and NATO M80 ball round will be simulated at muzzle velocity. During the simulation, the distribution of energy, stresses along the interfaces of different layers of materials, and residual velocity or penetration depth of the projectile will be obtained. Once confidence is established in the accuracy of the numerical simulation, the ballistic impact simulation and analyses of all the proposed six armor composite structures design will be carried out.

Based on the numerical models developed, a design optimization approach will be established, which will then be used to obtain the optimal design parameters of a ballistic protection composite structures. An approximate optimization method which has been successfully used in the solution of crashworthiness and impact design problems (see Yamazaki, K, Han, J., Ishikawa, H., and Kuroiwa, Y., Maximization of crushing energy absorption of cylindrical shells-simulation and experiment, Proceedings of the OPTI-97 Conference, Rome, Italy (1997); and/or Kurtaran, H, Omar, T. A., and Eskandarian, A., Crashworthiness design optimization of energy-absorption rails for automotive industry, Proceedings of 2001 ASME International Mechanical Engineering Congress and Exposition, New York, N.Y. (2001)) is used herein.

A design optimization problem of ballistic protection structure can be formulated as: Min: z(x)=ρ _(c) h _(c)+ρ₁ h ₁+ρ₂ h ₂ Subject to: U _(p)(x)−U _(T)(x)≦0 h _(il) ≦h _(i) ≦h _(iu), (i=1, 2, or 3)  (1) In this problem, the objective function z(x) is the area density of the armor, where x={x₁, x₂, x₃}={h_(c), h₁, h₂}. Also, h_(c), h₁, and h₂ simultaneously represent the thickness of the ceramic face layer, the intermediate layer, the backing layer, respectively; ρ_(c), ρ₁, ρ₂ are the densities of the ceramic layer, the intermediate layer, and the backing layer, respectively; and h_(il) and h_(iu) are the lower and upper boundaries on design variables hi. Additionally, U_(P)(x) is the displacement of a reference point at the back face of the projectile; U_(T)(X) is the distance of the back face of the backing layer to the reference point. Therefore, U_(P)(X)−U_(T)(X) gives the penetration distance of the projectile. To successfully contain the projectile, U_(P)(X)−U_(T)(X) must be less than zero. In order to avoid computationally intensive impact analysis, the objective and constraint function of above optimization problem will be approximated by their Response Surface (RS) approximation using Least-Square Method (LSM) as follows: $\begin{matrix} {{y(x)} = {a_{0} + {\sum\limits_{n = 1}^{N}{a_{n}x_{n}}} + {\sum\limits_{n = 1}^{N}{b_{n}\left( x_{n} \right)}^{2}} + {\sum\limits_{m = 1}^{N - 1}{\sum\limits_{n = {m + 1}}^{N}{c_{mn}x_{m}x_{n}}}}}} & (2) \end{matrix}$ where N is the constraint number and a, b, and c are the coefficients to be determined.

The analysis results are then used to create RS approximation through LSM. Consequently, the optimization problem of Equations (1) and (2) will be solved, and the resultant optimum solution will be verified by LSDYNA. If the predicted objective and constraints are identical with the results from LS-DYNA or the estimated optimum is satisfied enough, the optimization loop is stopped. Otherwise, the newly calculated results will be added to the design sets and a new optimization process will be carried out until the optimal solution is obtained.

A total of six exemplary composites structures with different backing composites combinations (see FIGS. 4 a to 4 f) have been disclosed. As is noted above, the present invention is not limited to just these six exemplary composites.

New composite technologies, such as braided and chain composites, have been recently developed and deployed in structural applications. Studies have demonstrated that these unique composites have great potential in damage tolerance and energy absorption. The combination of these novel composites with existing proven armor technology can, in some embodiments, provide a feasible and better solution of hybrid composite structures for ballistic protection. To date, no one has succeeded in applying hybrid materials and/or structures to structures for combat vehicle protection.

Light weight composite structures, as well as composite structures that withstand high energy absorption, are required for ballistic protection (armor) of military vehicles. Also of concern is the need for mobility and transportability of such composite structures (or even the vehicles and/or persons who might use such composite structures).

The following patents and publications are hereby incorporated by reference in their entireties:

[1] Binienda, W. K., High energy impact of composite structures—Ballistic experiments and explicit finite element analysis, Report, submitted to NASA Glenn Research Center, The University of Akron, Akron, Ohio (2004).

[2] Chocron-Benloulo, I. S., Sanchez-Galvez, V., A new analytical model to simulate impact onto ceramic/composite armors, Int. J. Impact Engng, vol. 21, 461-471 (1998).

[3] Cox, B. N., Sridhar, N., Davis, J. B., Mayer, A., McGregor, T. J., and Kurtz, A. G., Chain composites under ballistic impact conditions, International Journal of Impact Engineering, Vol. 24, 809-820 (2000).

[4] Gama, B. A., Bogetti, T. A., Fink, B. K., Yu, C., Claar, T. D., Eifert, H. H., and Gillespie, J. W. Jr., Aluminum foam integral armor: a new dimension in armor design,” Composite Structures, Vol. 52, 381-395 (2001).

[5] Gu, B. and Xu, J., Finite element calculation of 4-step 3-dimensional braided composite under ballistic perforation, Composites Part B 35, 291-297 (2004).

[6] Hogg, P. J., Composites for Ballistic Application, Composites Processing 2003, CPA, Bromsgrove, U.K. 21 Mar. 2003.

[7] Kurtaran, H, Omar, T. A., and Eskandarian, A., Crashworthiness design optimization of energy-absorption rails for automotive industry, Proceedings of 2001 ASME International Mechanical Engineering Congress and Exposition, New York, N.Y.

[8] Mayseless, M., Goldsmith, W., Virostek, S. P., and Finnegan, S. A., Impact on ceramic targets, J. of Appl. Mech., Vol. 54, 373-378 (1987).

[9] Navarro, C., Martinez, M. A., Cortes, R., and Sanchez-Galvez, V., Some observations on the normal impact on ceramic faced armors backed by composite plates, International J. Impact Engng., Vol. 13, 145-156 (1991).

[10] Qiao, P. Z. and Yang, M. J., Fatigue Life Prediction of Pultruded E-glass/Polyurethane Composites, Journal of Composite Materials, Vol. 40(9), 815-837 (2006).

[11] Roberts, G. D., Pereira, J. M., Revilock, D. M., Binienda, W. K., Xie, M., and Braley, M., Ballistic impact of braided composites with a soft projectile, NASA/TM-2004-212973 (2004).

[12] Sanchez-Galvez, V., and Galvez, D. F., Ballistic impact on ceramic/composite armors, In: Jounes N. et al. eds, Structures under shock and impact V. Computational Mechanics Publication; 673-681 (1998).

[13] Woodward, R. L., A simple one-dimensional approach to modeling ceramic composite armor defeat, Int. J. Impact Engng, Vol. 9, 455-474 (1990).

[14] Yamazaki, K, Han, J., Ishikawa, H., and Kuroiwa, Y., Maximization of crushing energy absorption of cylindrical shells-simulation and experiment, Proceedings of the OPTI-97 Conference, Rome, Italy (1997).

Although the invention has been described in detail with particular reference to certain embodiments detailed herein, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and the present invention is intended to cover in the appended claims all such modifications and equivalents. 

1. A hybrid composite armor structure comprising: at least one face layer, the face layer being formed from a ceramic layer; at least one backing layer, the backing layer being formed from at least one composite; and at least intermediate layer, the intermediate layer being positioned between the at least one face layer and the at least one backing layer.
 2. The armor structure of claim 1, wherein the at least one face layer is a ceramic tile layer.
 3. The armor structure of claim 2, wherein the at least one face layer is formed from an aluminum ceramic tile layer.
 4. The armor structure of claim 1, wherein the one or more intermediate layers are independently selected from composite backing layers, non-composite backing layers, and foam layers.
 5. The armor structure of claim 4, wherein the composite used in the composite layers is at least one fiber-reinforced composite.
 6. The armor structure of claim 4, wherein the foam is an aluminum foam.
 7. The armor structure of claim 1, wherein the one or more intermediate layers are independently selected from composite backing layers and non-composite backing layers.
 8. A hybrid composite armor structure comprising: at least one face layer, the face layer being formed from a ceramic tile layer; at least one backing layer, the backing layer being formed from at least one laminated composite or chain composite; and at least intermediate layer, the intermediate layer being positioned between the at least one face layer and the at least one backing layer, where the one or more intermediate layers are formed from a braided composite, stitched composite, or a foam layer.
 9. The armor structure of claim 8, wherein the at least one face layer is formed from an aluminum ceramic tile layer.
 10. The armor structure of claim 8, wherein the composite used in any one or more of the composite layers is at least one fiber-reinforced composite.
 11. The armor structure of claim 8, wherein the foam is an aluminum foam.
 12. A hybrid composite armor structure comprising: at least one face layer, the face layer being formed from an aluminum ceramic tile layer; at least one backing layer, the backing layer being formed from at least one laminated composite or chain composite; and at least intermediate layer, the intermediate layer being positioned between the at least one face layer and the at least one backing layer, where the one or more intermediate layers are formed from a braided composite, stitched composite, or a aluminum foam layer wherein the composite used in any one or more of the composite layers is at least one fiber-reinforced composite. 